The present invention relates generally to rotational position detectors. More specifically, the present invention relates to rotational position detectors employing both sensor winding and flux compensation windings. Methods for operating the rotational position detector are also disclosed.
The present invention claims priority from Japanese Patent Application 2002-089478, which was filed on Mar. 27, 2002, and which is incorporated herein by reference in its entirety.
Resolvers are employed in multiple applications, such as detecting rotational position. One type of resolver is a synchro signal generator where a signal is output from output windings. It will be appreciated that the frequency of the output signal is modulated according to the X and Y components of the rotational angle of a rotating element disposed within output windings. Such resolvers are often used in applications including the detection systems of conventional servomechanisms, trigonometric calculation devices, the control systems associated with automobile steering equipment, etc.
One example of such a resolver is a device known as a “variable reluctance resolver,” which has a structure such that a plurality of poles are formed on the fixed element, magnetizing windings and output windings are wound on the same poles of the fixed element, and the sum of the output windings on the plurality of poles is obtained as the output of a single output winding. In such variable reluctance resolvers, the output voltage, Vx, of the output winding that outputs the X-direction component of the rotating element is given by Equation 1 in which E sin ωt is the alternating current (AC) voltage, VP, applied to the magnetizing windings. Here, ω is angular frequency, which can be is represented by 2πf, where f is frequency, and K is a constant determined by the magnetizing windings, the output windings, and the characteristics of the rotating element and fixed element.Vx=K sin θ·E sin ωt  (Eq. 1)
In the same way, the output of the output winding that outputs the Y-direction component of the rotating element can be represented by Equation 2 because it is wound with a phase shift of 90° relative to the rotating element.Vy=K cos θ·E sin ωt  (Eq. 2)
The variable reluctance resolver includes a rotating element disposed in the center of a fixed element. It will be noted that the fixed element has a plurality of magnetic poles protruding from an annular (ring-shaped) yoke. Moreover, it has fixed-element windings wound on those magnetic poles. This structure is shown in FIG. 4, wherein fixed element 52 forms the annular shape, and rotating element 14, which is coupled to rotary shaft 13, passes therethrough.
In FIG. 4, magnetic pole teeth 4 of fixed-element core 1 are formed on the inner side of fixed element 52 and are made to face the surface of the outer side of rotating element 14. A plurality of fixed elements on which fixed-element windings 50 are wound are formed on the entire inside perimeter of fixed-element core 1. Rotating element 14 is inserted into the inside of fixed-element core 1, and the rotational angle of that rotating element 14 is detected by methods that are well known to one of ordinary skill in the art.
It will be appreciated that the structure depicted in FIG. 4 is difficult to repair. In other words, fixed-element 14, coupled to rotary shaft 13, passes through the inside of fixed element 52, which forms an annular shape. As a result, in cases where the fixed element 52 must be changed due to damage, such as impact damage to the fixed element 52 from an accident, a broken wire in fixed winding 50, insulation failure, etc., it is necessary to remove the rotary shaft 13 to take off fixed element 52. Moreover, because rotary shaft 13 is attached to other equipment, in some cases it is necessary to disassemble that equipment before it is possible to remove the rotary shaft 13. As a result, a lengthy change out time with a commensurate large labor expense may be incurred in order to replace fixed element 52.
Several resolver designs are known that, in order to achieve reduced size of the resolver, do not form a closed magnetic path around the entire periphery of the rotating element. For example, Japanese Unexamined Patent Application Publication H5-252711 discloses a resolver in which the yoke of the detection head consists of two mutually parallel yokes, formed along the direction of travel of the inductor and joined by means of a connecting part at the center to form a shape like the letter H. The magnetic pole teeth formed at both ends of it and the iron core teeth of the inductor are placed in opposition. Thus, two magnetic circuits are formed between the inductor and the detection head so that a permeance change generates a 90° phase difference. It will be appreciated that permeance is a measure of the ability of a magnetic circuit to conduct magnetic flux; thus, it is the reciprocal of reluctance. In contrast, WO 02/25216 A1 discloses a resolver in which, if the motor pole logarithm is n, a detection part is positioned relative to the rotor within a probability range of 2p/n.
Moreover, Japanese Unexamined Patent Application Publication 2002-168652 discloses a nX reluctance resolver that is configured from an inductance type rotor, rotating about a rotational axis, and a stator. The stator core comprises a yoke shaped as a circular arc, positioned within an angular range for a mechanical angle of 360°/n (where n is a positive integer greater than or equal to 2), and 4×k magnetic pole parts (where k is also a positive integer but k is greater than or equal to 1), connected to the yoke and arranged at specified intervals. On each magnetic pole, a magnetizing winding is wound. On every other magnetic pole part, i.e., on odd numbered poles, a first detection-use winding is wound, while on the remaining every other magnetic pole parts, i.e., on even numbered poles, a second winding is wound, which second windings are also employed in position detection.
It will be appreciated that in the reduced size resolvers discussed immediately above, the magnetic flux at the ends of, for example, the arcuate yoke varies with respect to that in the vicinity of the central windings. It will also be appreciated that this variable flux profile reduces the accuracy of these abbreviated resolvers as compared to resolvers employing annular yokes. What is needed is a resolver employing an arcuate or partial yoke that is not subject to flux profile variations.